a) Field of the Invention
The present invention relates to a vacuum capacitor and its manufacturing method for the same, the vacuum capacitor being suitably used for an oscillation circuit of a high power transmitter, a high-frequency power supply of a semiconductor manufacturing device, or a tank circuit of an inductive heating device.
b) Description of the Related Art
A previously proposed vacuum capacitor includes an insulating envelope made of ceramics or glass having upper and lower ends to which upper and lower end electrodes each made of copper are hermetically sealed via upper and lower metal fittings so that a vacuum vessel is formed. A plurality of copper made, cylindrically shaped electrode plates of different diameters are extended vertically from an inner surface of the upper end electrode concentrically at equal intervals to form first cylindrical electrodes.
In addition, another plurality of copper made, cylindrically shaped electrode plates of different diameters are extended vertically from an inner surface of the lower end electrode and interposed between each of the first cylindrical electrodes to form second cylindrical electrodes.
It is noted that a hole is penetrated through a center portion of the upper end electrode to be used for exhausting air from the vacuum vessel described above, an exhaust tube made of copper is fitted around the hole, and an exhaust tube cover covers the exhaust tube is screwed into a tap hole installed on an outer surface of each end electrode.
Next, a previously proposed manufacturing method will be described below.
First, a plurality of concentrically arranged circular grooves are provided on the inner surface of the lower end electrode. Each cylindrical electrode plate constituting the second cylindrical electrode is mounted on the circular groove so that each cylindrical electrode plate is concentrically arranged. Thereafter, each cylindrical electrode plate is brazed or welded to the lower end electrode.
Thereafter, the metal fittings are conjoined to the respective ends of the insulating envelope.
Thereafter, another plurality of concentrically arranged circular grooves are formed on the inner surface of the upper end electrode. Each cylindrical electrode plate constituting the first cylindrical electrode is mounted on the circular groove so that each cylindrical electrode plate is concentrically arranged. At this time, the exhaust tube is fitted around the hole. The upper end electrode, each cylindrical electrode plate, and exhaust tube are brazed or welded.
Next, the insulating envelope with the respective metallic fittings are mounted on the inner surface of the lower end electrode having the cylindrical electrode and the inner surface of the upper electrode with the one metallic fittings having the cylindrical electrode and exhaust tube is mounted on the inner surface of the lower end electrode. Then, a plurality of jigs to concentrically arrange the end electrodes are fitted into the inner surface of the upper end electrode.
In this state, the brazing or welding is performed between the metal fitting and the upper end electrode and between the metallic fitting and the lower end electrode.
Next, a vacuum exhaust device is attached to the exhaust tube, a heat vacuum is performed with the vacuum vessel, and, thereafter, the exhaust tube is pinched to be hermetically sealed.
It is noted that the circular groove may not be provided on the lower end electrode and, in place thereof, a convex portion may be provided on a center portion of the inner side of the lower end electrode, a letter-U shaped portion which is bent in the inner side of a diameter direction is provided on a junction end between each cylindrical electrode plate constituting the second cylindrical electrode and the end electrode is provided, and each cylindrical electrode plate may concentrically be arranged so that the letter-U shaped portion is fitted to the convex portion and adjacent letter-U shaped portion. The same thing is applied equally well to the upper end electrode.